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# PS : Mean & SD

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Manager
Joined: 22 Mar 2010
Posts: 59
Followers: 1

Kudos [?]: 27 [0], given: 1

PS : Mean & SD [#permalink]

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17 Aug 2010, 12:35
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Difficulty:

(N/A)

Question Stats:

83% (01:20) correct 17% (03:39) wrong based on 6 sessions

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If a sample of data has mean of 20 and SD of 3, which of the following values is more than 2.5 SDs from the mean?

a. 12
b. 13.5
c. 17
d. 23.5
e. 26.5
[Reveal] Spoiler: OA
Math Expert
Joined: 02 Sep 2009
Posts: 37590
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Kudos [?]: 99595 [1] , given: 11023

Re: PS : Mean & SD [#permalink]

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17 Aug 2010, 12:43
1
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Expert's post
EnterMatrix wrote:
If a sample of data has mean of 20 and SD of 3, which of the following values is more than 2.5 SDs from the mean?

a. 12
b. 13.5
c. 17
d. 23.5
e. 26.5

Value is more than 2.5SD from the mean means that the distance between the mean and the value must be more than 2.5SD=7.5. So the value either <20-7.5=12.5 or >20+7.5=27.5.

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Manager
Joined: 20 Jul 2010
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Kudos [?]: 71 [0], given: 32

Re: PS : Mean & SD [#permalink]

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17 Aug 2010, 12:48
Yep. I agree. The standard deviation is the deviation from the Mean.

2.5 SD's mean is equal to: +/- 2.5*3 = +/- 7.5

ie. 12.5 to 27.5

Re: PS : Mean & SD   [#permalink] 17 Aug 2010, 12:48
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